1. Field of the Invention
The invention generally relates to a filter, and particularly to a low-pass filter.
2. Description of Related Art
It is well-known that a filter is able to eliminate interference signals for a communication product. Features of an ideal filter are that signal attenuation is zero within a pass band and becomes infinite within a cut-off band, and a transition from the pass band to the cut-off band should be as sharp as possible, so that a distance between a transmission zero and the cut-off band is as short as possible. However, an unneglectable problem is, as the transmission zero and the cut-off band become closer, an insertion loss may correspondingly increase.
Therefore, a heretofore unaddressed need exists in the industry to overcome the aforementioned deficiencies and inadequacies.